| Abbreviation | Definition |
|---|---|
| OOC | Out Of Conference |
| OOG | Object Orientation Game |
| OOG | Out Of Game |
| OOK | Omituisten Otusten Kerho (Finnish Gaming Clan) |
| OOL | Official OOTP (Out Of The Park) League |
| OOO | Oscuro's Oblivion Overhaul |
| OOP | Object Of Play |
| OOP | Out Of Play |
| OOTF | Officials on the Field |
| OP | Open Position |
| OPL | Old Parochial League |
| OPP | open public pool |
| OPP | Opponent |
| opp. | opposition |
| OPR | Official Poker Rankings |
| OPRA | Outdoors Program Recreational Athletics |
| OPS | OBP (On Base Percentage) Plus SLG (Slugging Percentage) |
| OPS | Online Premium Services |
| OPSC | Oak Park Sportsmen's Club |
| OPSC | Overland Park Soccer Club |